The present invention pertains generally to an arrangement of contacting elements or contacts assembled into a probe for electrically connecting a test system to the contact pads on a semiconductor device to be tested. More specifically, the invention relates to test probes for contacting rows of densely spaced bonding pads such as on memory devices on a wafer.
A large portion of the silicon chip industry utilize cantilevered beam probes to make electrical contact to the devices on a wafer. Cantilevered beam probes make electrical contact to pads typically made of aluminum, which are usually located on the perimeter of a device or arranged in a single or double row in the center of a device. Generally, cantilevered beam probes are capable of contacting pads that have a center-to-center spacing or pitch as low as 75 microns. However, one important disadvantage of cantilever beam probes is they cannot be used to contact more than a double row of pads since the beams would interfere with each other. This problem also limits cantilever probes for testing more than one chip at a time.
Vertical probes are typically utilized to overcome the disadvantages of cantilever probes because the probes do not interfere with each other. A typical vertical probe is the Cobra probe which is described in U.S. Pat. No. 4,027,935. This probe consists of an upper and lower die which supports the contacts that are formed from a 125 micron diameter wire. The contacts are generally sharpened to a fine point on the center axis of the wire, like a pencil point. This tip shape both improves the ability to penetrate aluminum oxide on the device pad and has the relative effect of enlarging the pad size. In other words, the fine tip makes it easier to hit the pad within the allowable window. The larger the tip, the more likely it is to contact the area outside of, or miss the targeted window. Currently, 125 micron vertical probes are capable of contacting an array of pads on a 225 micron pitch. In order to be able to contact pads with a smaller pitch, thinner wire on the order of a 100 microns or less can be used to form the contacts, but has the disadvantage of less strength and more difficult handling. Furthermore, thinner wire increases the tendency of the contacts to fail mechanically. Thus an improved probe is needed to overcome these and other disadvantages of the prior art, and is provided by this invention.
The present invention overcomes these and other disadvantages of the prior art, by providing in one aspect a probe system comprising a plurality of probes having a center axis, with each probe having a tip offset from the probe axis. The offset tips of the probes are arranged in two parallel rows for contacting a row of pads with the tip of each probe oriented adjacent the centerline between the two rows of probes.
In accordance with another aspect of the invention, a probe system for contacting a row of pads is provided comprising a housing having an upper die, a lower die, and a plurality of probes having a center axis. Each probe has a tip for contacting a pad. Each probe has a first end pivotally mounted in a hole of the upper die and a distal end extending down from the upper die into a hole of the lower die. The lower die holes with the probe tips mounted therein are arranged in two parallel rows with each probe tip oriented on the centerline formed between the two rows of probe tips.
In accordance with another aspect of the invention, a probe system for contacting a row of pads is provided comprising a housing having an upper die, a lower die and a plurality of probes each having a center axis. Each probe has a distal end having a tip for contacting a pad. Each probe has a first end pivotally mounted in a hole of an upper die and a distal end extending down from the upper die and into a hole of the lower die. The upper die holes are arranged in two parallel rows in a staggered configuration. The lower die holes with the probe tips mounted therein are arranged in two parallel rows with each probe tip oriented on the centerline between the two rows of probe tips.
In accordance with yet another aspect of the invention, a probe for contacting a pad is provided comprising a probe having a center axis and a second end. The second end has a bevel to provide a tip offset from the center axis and is located along the probe periphery.
In accordance with still another aspect of the invention, a probe for contacting a pad comprising a probe having a center axis and a second end. The second end has a first and second bevel to provide a tip at the apex of the intersection of the first and second bevels. The tip is offset from the center axis and is located along the probe periphery.